TV is UE325520RW (CN01,LD320BGC-01) FW 1025 (PVR was enabled)
TV bebooted by itself while installing one of the SmartHub application updates. After is that started to reboot every several minutes. And now it powers on just after a power plug is connected showing a boot logo and a black screen in cycle. It is not even possible to get into a service menu mode.
PSU board looks really god with no visual signs of capacitors weared off or power harness to mainboard overheated. I also tried to make a EEPROM reset but it didn't help though i just used two wires with no soldering. I'm going to change the EEPROM chip, but I did not backed up the service menu parameters before. Can anyone help me with the default parameters for this model?

Service said the mainboard must be changed - $200.Will any BN41-xxxx mainboard from be compatible with the rest of the TV? I can see two offers from UK models (5520RK) from 37" and 32" models only. Or maybe it can be upgraded to 6xxx series that way?

i`m not sure about upgrade to D6 series, here is no info the boards are crosscompatible. But second hand mainboard isn`t as expensive as you just told. You can search for mainboards from 32-46 inc models and they should work as native one.

Nope, there was a 2-year warranty.
I found at ebay two options from the UE32D5520 and one from the UE37D5520RK (from the UK models).
They both looks very similar like my one, but the part number is different. Will they work and do they need any calibration?

I was curious if my TV had a firmware update and I saw that it did. I was curious what that update was for so I tried finding some official changelog. As I'm sure you can guess... I couldn't find one. Googling eventually brought my attention to this site.

I had no idea my TV could be rooted. That's cool.

But (and please forgive me for this question that is sure to be thought of as "stupid" by people familiar with all of this) what seems to be missing from the WIKI is... why? What I'd like to know is what benefits, specifically, I might get if I go through the risk, trouble, and (due to my firmware version) donation expense?

Can you give me some examples of what I can do with my rooted TV? Just give me some highlights please, if you don't mind.

I have ue50d5500 and also is bootloop. The first mainboard starts normally, you can change channels, volume, but exactly 6 seconds reboots. The second mainboard only logo Samsung SmartTV and reboot. Both the original firmware. On one did reaball processor and ram - no improvement.
the processor heats strongly - perhaps there is a problem.

The question of whether you can replace the mainboard in the series D6xxx? Series d5xxx now I can not find second-hand in Poland

your problem on both mainboards - authduld. One or more partitions does not match checksums and tv reboots again and again.
The second mainboard whose log is attached here probably has problem with kernel (checksums again...). So the solution only as you said mainboard replacement. No idea about is it possible to upgrade to D6 or not. No experience. But theoretically it may work...